The specific aim of this study is to use Emergency Room records for the surveillance of changes in states of health in relation to changes in air pollution. Changes will be considered in terms of two groupings of time intervals: 1) the short cyclic variations in air pollution over days, weeks and months; 2) the predicted long-term decline in levels of air pollution in New York City that began with policies inplemented in January, 1967. In order to study the separate and combined effects of weather and pollution on health, two areas similar in demographic characteristics and exposed to the same weather, but differing in their air pollution levels, are being studied. The study covers a 3-year period (1969-1971) during which 40 air pollution monitoring stations have been in operation and new air pollution control measures have been taken.